CLONAL STABILITY AND MUTATION IN THE SELF-FERTILIZING HERMAPHRODITIC FISH, RIVULUS-MARMORATUS

Previous investigations of natural populations of the hermaphroditic, self-fertilizing fish species Rivulus marmoratus demonstrated a surpri sing amount of interclonal differentiation among highly polymorphic '' DNA fingerprint'' loci. The genetic differentiation observed among clo nes was thought to be the effect of extreme population mixing because of high rates of migration and population extinction. It was demonstra ted that mutation rates at hypervariable loci would have to exceed 10( -4) on average to alone account for the observed interclonal differenc es. The present study reports that, among laboratory lines oi this spe cies, mutation rates at the most unstable set of hypervariable loci ar e not greater than 3.52 x 10(-4), and are probably lower. Mutation rat es at several other sets of loci are even lower. A field transplantati on study demonstrated complete clonal stability over several generatio ns. These results suggest that the high interclonal differences observ ed in natural populations of this species is not caused by a generally higher rate of mutation at these specific loci.